package org.apache.lucene.search;

/**
 * Copyright 2004 The Apache Software Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import org.apache.lucene.index.IndexReader;
import java.util.BitSet;
import java.util.WeakHashMap;
import java.util.Map;
import java.io.IOException;

/**
 * Wraps another filter's result and caches it.  The caching
 * behavior is like {@link QueryFilter}.  The purpose is to allow
 * filters to simply filter, and then wrap with this class to add
 * caching, keeping the two concerns decoupled yet composable.
 */
public class CachingWrapperFilter extends Filter {
    private Filter filter;

    /**
     * @todo What about serialization in RemoteSearchable?  Caching won't work.
     *       Should transient be removed?
     */
    private transient Map cache;

    /**
     * @param filter Filter to cache results of
     */
    public CachingWrapperFilter(Filter filter) {
        this.filter = filter;
    }

    public BitSet bits(IndexReader reader) throws IOException {
        if (cache == null) {
            cache = new WeakHashMap();
        }

        synchronized (cache) { // check cache
            BitSet cached = (BitSet) cache.get(reader);
            if (cached != null) {
                return cached;
            }
        }

        final BitSet bits = filter.bits(reader);

        synchronized (cache) { // update cache
            cache.put(reader, bits);
        }

        return bits;
    }

    public String toString() {
        return "CachingWrapperFilter(" + filter + ")";
    }

    public boolean equals(Object o) {
        if (!(o instanceof CachingWrapperFilter))
            return false;
        return this.filter.equals(((CachingWrapperFilter) o).filter);
    }

    public int hashCode() {
        return filter.hashCode() ^ 0x1117BF25;
    }
}
